Effect of the Disordering of Thin Surface Layers on the Electronic and Optical Properties of Si(111)
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ACES, INTERFACES, AND THIN FILMS
Effect of the Disordering of Thin Surface Layers on the Electronic and Optical Properties of Si(111) B. E. Umirzakova, D. A. Tashmukhamedovaa,*, A. K. Tashatovb, N. M. Mustafoevab, and D. M. Muradkabilova a Tashkent b
State Technical University, Tashkent, 100095 Uzbekistan Karshi State University, Karshi, 180003 Uzbekistan *e-mail: [email protected]
Received May 20, 2020; revised July 13, 2020; accepted July 20, 2020
Abstract—The degree of disordering and the thickness d of disordered layers and their effect on the band gap Eg of single-crystal Si(111) under Ar+-ion bombardment are studied for the first time. It is shown that the d value at ion energies of E0 = 1 and 2 keV is ~(100–120) and ~(150–160) Å, respectively. In this case, the density of states of electrons in the Si(111) valence band significantly changes, the light transmittance decreases to K = 55–60%, and the Eg value increases by ~10%. Under Ni+-ion bombardment, surface disordering is accompanied by a sharp change in the composition of the surface layers and, as a result, the K value decreases to 5–10%. After heating at T = 900 K, nanocrystals (at doses of D ≤ 1015 cm–2) and NiSi2 nanofilms (at D = 6 × 1016 cm–2) are formed. Keywords: ion bombardment of Si, electronic properties, optical properties, thin layers, annealing 10.1134/S1063782620110263
1. INTRODUCTION At present, much attention is paid to studying the optical and electronic properties of semiconductors with nanophases and nanofilms in the surface layers. Of particular interest are investigations of the variation in the properties of silicon with sizes of several nanometers and studies aimed at controlling the properties of Si nanofilms affected by various factors (adsorption of atoms, ion and electron bombardment, and oxidation). In [1–7], it is shown that increasing porosity, decreasing sizes, and a change in the shape of silicon nanophases shift the light absorption edge toward higher energies, which is explained by an increase in the band gap Eg. The maximum (up to 1.7 eV) growth of the Eg value is observed at a size of the nanocrystalline Si phase of ≤ (3–4) nm [2, 8]. In addition, an increase in the Eg value to 1.9 eV is observed in the case of the formation of thin amorphous silicon films [6]. Therefore, the amorphous silicon/nanocrystalline silicon system is promising for the development of highefficiency solar cells [9, 10]. The formation of various defects and nanoscale structures in Si during the ion implantation and deposition of atoms of different elements and their effect on the physical properties of Si were studied in [11, 12]. In particular, in [11], it was shown that the defect layer
with deep levels, which occurs due to the chemical interaction of Pd with Si at 100°C, extends to a depth of 1 μm. In [13–16], the effect of low-energy ion implantation on the crystal and electronic structures of Si, GaAs, and CaF2 single crystals was investigated. It was shown that this process is accompanied by disordering of the surface layers and the format
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